On Married at First Sight's tenth season, Zach admitted to Mindy he had been having conversations both via text and on the phone with her close friend Lindsay -- but only after Mindy asked him if he had been in touch with any of her pals after the wedding.
Zach claimed he had confided in Lindsay and she had given him advice on how to deal with Mindy and proceed in his marriage.
Mindy was blown away both Zach and Lindsay had been hiding their alleged friendship from her, and since both parties deleted their text chains, Mindy assumed one or both of them was lying about what they had discussed.
When Zach appeared on the March 18 broadcast of Married at First Sight: Unfiltered, host Jamie Otis noted it was understandable why Mindy was "so suspicious" of his interactions with Lindsay.
"Did you ever get the feeling Mindy's friend was texting you for more than just helping out her friend?" Jamie asked.
"Umm, I'm incredibly naive when it comes to stuff like this, in a lot of situations," Zach replied.
"I didn't feel that because I was so focused on, 'Here is the reason, the reason we're talking, and I need answers.' I had no idea if there was a motive there."
But Pastor Cal clearly wasn't buying what Zach was selling.
"My man, Zach. Zach, Zach, Zach," Pastor Cal quietly said in a condescending tone.
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"Zach. Zach Justice," Pastor Cal repeated. "I mean, you're a good looking guy -- you and your friend, your hair. Okay? Great shape! I wish I had your abs."
"Same," Jamie added.
"You know when a woman is coming onto you," Pastor Cal insisted. "Right or wrong?"
"Yeah," Zach confessed.
"Okay, there is no way in Hades, okay," Pastor Cal began with a laugh, "that I'm going to allow anyone to instruct me about my wife without my wife knowing. That is a cardinal sin!"
Pastor Cal added, "And [Mindy] should have been completely more upset than she actually was. And I think you know that now!"
"Oh yeah," Zach noted, "very much so."
Pastor Cal went on to explain there is "a Guy Code and then a Husband Code."
"You broke them both!" Pastor Cal said, which prompted laughter from Zach.
Zach told Mindy on Married at First Sight 10 he had only talked to Lindsay once on the phone before and hadn't spoken to her in days, but Mindy heard a different story once she confronted Lindsay about what was going on.
While chatting over the phone, Lindsay insisted she and Zach had spoken on the phone two or three times up to that point and he had actually just texted her that morning.
Mindy asked if Zach had reached out to Lindsay "for the hell of it" or to sincerely talk about Mindy, and Lindsay replied, "I think both. I felt like we were building a friendship outside of just you."
"I would immediately talk to the friend and be like," Katie began.
"F you!" Jamie yelled and interjected.
"What are you doing?" Katie continued. "What are you doing? I can see on Zach's end how he maybe didn't know where the motive was coming from, but you should've found out what the motive was."
As Katie shared her opinion, Pastor Cal argued quietly in Katie's ear, "Don't take it easy on him. Don't take it easy on [Zach]. Don't do that."
"I'm not," Katie countered. "He should've found out what the motive was."
Zach and Lindsay's alleged friendship became even more suspicious in Mindy's mind when Lindsay claimed she was learning how Zach "manipulates things."
"So I said, 'I'm not going to talk to you again until filming is over,' like, 'We're done,'" Lindsay recalled telling Zach.
Mindy found it strange in itself Lindsay apparently intended to resume talking to Zach once filming ended, but Lindsay assured Mindy that she would block his number.
"I should [block him]. You're 100 percent right. I can do that right when I get off the phone with you. I have no interest in ever talking to him again. I think he's a liar and a sociopath," Lindsay told Mindy.
Zach and Mindy therefore chose to stay together on "Recommitment Day," despite Pastor Cal's concerns Zach was on the show for the cameras and to build his fitness or modeling career.
Although Zach promised to be honest going forward and put more noticeable effort into his relationship, the episode ended with him refusing to sleep in the same bedroom as Mindy, leaving her feeling rejected and alone, once again.